Preheat the oven to 400 degrees F. Lightly grease an 8-inch square cake pan.
In a large bowl, whisk the dry ingredients -- flour(s), baking powder, baking soda, and salt.
In a medium bowl, whisk the wet ingredients -- the maple syrup, egg, milk, and olive oil.
Pour the maple syrup mixture into the flour mixture and gently mix together until just combined. Gently fold in the blueberries.
Pour the batter into the prepared pan. Bake until golden brown and a toothpick inserted into the middle comes out clean - about 30 minutes.
While the cake is baking, prepare the glaze ingredients.
Let the cake cool slightly in the pan on a wire rack. If you are going to glaze the cake, set the wire rack over a parchment-lined sheet pan. Once the cake is slightly cooled, run the tip of a knife or spatula around the sides to loosen it. Place a plate over the cake and flip it over onto the plate, tapping the sides and bottom of the pan to make sure the cake is free. Remove the pan, turn the cake over and place it back on the wire rack over the sheet pan. (or put it directly on a serving platter)
If using the glaze, place the butter in a small microwaveable bowl, melt in the microwave. Then add the syrup, powdered sugar and pinch of salt and mix well.
Poke holes in the cake with a toothpick or thin skewer, then pour the warm glaze over the cake, letting the excess glaze drip onto the baking sheet or serving platter. If you poured it over parchment, once you place the cake on its serving platter, you can carefully lift the parchment and pour the rest of the glaze over the cake. Slice and serve.